“Identification of molecular mechanisms associated with increased yield caused by mechanical treatment in Arabidopsis thaliana”

RAMINGER BETINA LORENA; CHAN, RAQUEL LÍA; CABELLO, JULIETA VIRGINIA

Mendoza

Congreso; SAIB; 2022

Observations on Arabidopsis thaliana have shown that an increase in stem diameter accompanied by an increase in the number of vascular bundles leads to significant improvements in seed production. These characteristics have been achieved by adding a 1.5 g of hanging weight placed at the apex of the 4 cm tall Arabidopsis floral rod for 48 H. This treatment generates an increase in the number of vascular bundles by duplicating existing ones, so similar to when a branch of the floral stem is going to be generated, and it occurs from the apex to the base, that is, in the same direction as the auxin flow. This hormone is essential for the response to treatment and new bundles generation. Other hormones, such as brassinosteroids (BS) or strigolactones (SL) are also involved.We initially studied the participation of the BS. Mutants in signaling pathways of this hormone, bes1 and bzr1, didnot respond to weight treatment and the exogenous addition of brassinazole (an inhibitor of brassinosteroid biosynthesis) in WT plants interrupts their response.BS, SL and auxins also regulate the transcription factor BRC1. This is a negative regulator of branching and a positive regulator of cle44 peptide expression, which participates in the proliferation and differentiation of procambium cells. brc1, cle44 and max4 mutants did not respond to weight treatment neither with the sparsely branched ecotype of Arabidopsis, Zurich (Zu-0). Brc1 and max4 mutants and Zu-0 ecoptype did not increase seed production, while cle44 mutant decreased it significantly after weight treatment. In WT plants, weight treatment also generated an increase in photosynthates transport from source to sink tissues, induced genes that encode to enzymes participating in synthesis and degradation pathways of starch and sucrose transporters genes. In addition, these plants had a higher concentration of lipids in seeds, while the opposite occurs in cle44 mutants, which showed a decrease in sucrose transport, lower production and lower lipids concentration in seeds after treatment. Roots were also affected by weight treatment, which in WT plants generated an increase in main root diameter and vascular bundles number, an increase in the total root biomass and improved sucrose transport by phloem tissue.Finally, the effects generated by weight treatment in Arabidopsis were also reproducible in other dicotyledonous plants with monopodial architecture such as chia and tomato.These results allowed us to conclude that phytohormones such as AUX, BS and SL were necessary but not sufficient for the complete response to mechanical treatment with increased seed production, which would also imply the activation of molecular pathways related to branching and vascular development, and affect not only the aerial part of the plant but also the root. Weight treatment also caused modifications in carbon partitioning and lipid accumulation in seeds of WT plants, while the opposite occurs in cle44 mutant plants.